This invention relates to a drive train for a power take off shaft, and particularly to a drive train for the power take off shaft of an agricultural tractor.
Agricultural tractors are generally provided with at least one power take off shaft in order that implements, such as rotary harrows, fertilizer spreaders, sprayer pumps, balers, etc. may be driven.
Implement manufactures now manufacture tractors and implements to run at one of three standard speeds, namely, 540 rpm, 1000 rpm, and ground speed. The term xe2x80x9cground speedxe2x80x9d means that the rate of rotation of the power take off shaft is proportional to the speed at which the tractor travels across the ground.
Since implements are manufactured to these standards, it is necessary for tractors to be provided with power take off shafts which rotate at the required speed. Power take off gear trains have been developed which provide for the selection of different speeds, eg 1000 rpm, 540 rpm, ground speed. Clearly, in the case of a fixed rotation speed, i.e. 1000 rpm, or 540 rpm, this can only be achieved at a certain engine speed. The manufacturer selects this speed, and usually a speed towards the maximum engine speed is selected, thereby permitting engine speed to fall as load on the power take off shaft increases.
Where the load on the power take off shaft is relatively low, the torque back up provided by running the engine at a high speed is not required. It is therefore not efficient to run the engine at high speed, but this is required in order for the power take off shaft to rotate at the required speed. In order to overcome this problem, manufacturers often provide what is known as a 540 rpm economy power take off shaft. Effectively, the gear train is arranged such that the power take off shaft runs at 540 rpm with an engine speed of about two thirds maximum speed, and as such the tractor""s fuel economy improves axed the engine is quieter.
Gear trains for power take off shafts, where the power take off shaft can be selectively engaged to rotate at 540 rpm, 1000 rpm, and either ground speed or 540 rpm economy, are known. In one known gear train, separate power take off shafts are provided.
The power take off gear train is usually housed in a transmission casing. Space in such casings is limited. The invention provides an arrangement which.provides for selection of power take off output speed between 540 rpm, 1000 rpm, and either 540 economy, or ground speed using a small number of pats in a minimum of space.
Rated speed means the engine speed at which the power take off runs at the specified speed in revolutions per minute.
The invention provides a power take off drive train for an agricultural tractor, the drive train comprising at least one input shaft and an output shaft, said shafts being rotatably mounted in a transmission casing, wherein the gear train provides for the output shaft to be rotated at one of three selected speeds, one of the at least one input shafts mounting first and second input gear wheels and a selector, the gear wheels being free to rotate on the shaft, and wherein the selector is mounted on the shaft for rotation therewith, and to slide axially along the shaft to engage with one of the first and second gear wheels transmitting torque thereto, and wherein the output shaft mounts first and second output gear wheels fixed for rotation therewith, the first and second output gear wheels being in driving engagement with the first and second input gear wheels respectively, and wherein the drive train further comprises a third output gear wheel, which gear wheel engages with a third input gear wheel mounted on an input shaft mounted in the transmission casing, wherein drive to the output shaft through the third input and output gears is selectively engageable by means of a selector, and wherein the third output gear wheel is mounted on one of the first and second output gear wheels.